In the correction of alignment and positioning of maloccluded teeth, various mechanical arrangements are used for applying steady forces to the teeth over a prolonged period of time such that the teeth are urged into an aligned disposition within the oral cavity. Typically, brackets are fastened to certain teeth and then a wire arrangement, referred to as an archwire, is fastened to the brackets to apply forces in appropriate directions so as to urge the affected teeth into a different positional orientation. The archwire is commonly drawn from stainless steel, and it is important that it possess properties of flexibility so that it can be bent into a desired shape, while at the same time exhibiting sufficient stiffness and resiliency (inherent memory property) such that desired forces are imparted upon the teeth to be repositioned.
In the past, orthodontists have primarily employed solid or stranded stainless steel or metal alloy wires having either a circular or rectangular cross section in fabricating orthodontic archwires. The word rectangular as used herein also includes a square cross section. While stainless steel archwires of a given diameter, i.e., typically in the range of 0.016 to 0.022 inches, and rectangular archwires of various sizes, are commonly employed, they suffer from a lack of flexibility because the outside diameter is necessary to ensure that the wire will have the requisite resiliency to provide the desired forces upon the teeth. While reducing the diameter may render the wire more flexible, its resiliency is correspondingly reduced such that the wire is subject to permanent deformation and/or breakage. More recently, an archwire formed from a nickel titanium alloy and sold under the trademark "Nitinol Activ-Arch" by the Unitek Corporation of Monrovia, Calif., has been introduced which posseses the desirable characteristics of reduced stiffness (greater flexibility) and high resistance to deformation as compared to stainless steel archwire of comparable dimensions. The use of archwires of Nitinol alloy in orthodontia is described in U.S. Pat. No. 4,037,324.
In addition, orthodontic work is frequently performed on patients who may be somewhat self-conscious over their appearance and are, at times, embarrassed by the presence of the orthodontic appliances of their teeth. Stainless steel wires of a requisite diameter tend to be somewhat unsightly. U.S. Pat. No. 4,050,156 suggests coating a stainless archwire with a plastic matrix in which a suitable colorant is intermixed so as to match the natural tooth color of the patient. Here, however, the plastic material is not used as a structural member as in the present invention, but is only used as a method of applying a colorant to a stainless steel surface.